Cl Kβ (K-V) emission of CFCl3 excited by synchrotron radiation below and above Cl-1s binding energy: perturbation effects in a highly excited neutral molecule

Abstract

The Cl Kβ (K-V) fluorescent emission and K absorption spectra from CFCl3 vapor were measured using monochromatic synchrotron radiation. Weak supra-threshold features were observed in the Cl K absorption spectrum. The Cl 1s binding energy of CFCl3 was estimated to be 2829.4eV. A comparison of the Cl Kβ (K-V) emission spectrum excited at 2833.5eV (K + 4eV) photon energy with the Kβ spectrum excited at 2880eV (K + 50eV) photon energy indicated an increase of emission intensity from multiple vacancy transitions. The Cl K absorption has a discrete absorption maximum (or a "white-line") at 2822.6eV, the transition of a Cl 1s electron to the first allowed unoccupied MO. For the first time an X-ray emission spectrum was obtained with excitation below the ionization threshold. Features in the 2822.6eV excited (an exciton state, i.e., a highly excited state of the neutral molecule) Cl Kβ (K-V) spectrum were observed to have significant intensity changes and relative energy position shifts from the emission spectrum excited above the Cl 1s threshold. These differences are explained in terms of perturbation effects due to the presence of an electron in the first unoccupied MO.